Treatment of substrates, particularly polymeric subtrates, with low pressure ionized gases or "plasmas", has widely been reported to produce alterations in the substrate surfaces which are desirable for certain applications. For example, plasma treatment may reduce surface contact angles, improving wettability of the surface and/or bondability with certain adhesives, and may also effect cross-linking of the substrate material. Use of certain polymerizing gases may also allow the substrates to be coated with very thin layers of polymer. Other uses for plasma treatment are described in Gombotz et al, "Gas-Discharge Techniques For Biomaterial Modification", CRC Critical Reviews in Biocompatibility, 4, pp. 1-42 (1984).
In co-pending application Ser. No. 07/754,326, filed Sep. 4, 1991, as a continuation of Ser. No. 07/457,019, filed Dec. 26, 1989, incorporated herein by reference, it is disclosed that silicone rubber tubing employed as a component of heart pacemaker leads has a tendency toward surface blocking. Surface blocking is a phenomena which can result in adjacent implanted leads sticking to each other instead of moving independently within the body, thereby increasing the risk of dislodgment of the leads. The referenced application discloses that plasma treatment of the silicone tubing used in forming such leads reduces blocking, rendering pacemaker leads manufactured therefrom more able to slip against each other within the body.
The present invention pertains to an apparatus which is particularly useful for treating implantable lead materials as described in Ser. No. 07/754,326, but also has application for treatment of other strip-stock material which may be desired to be plasma treated for any purpose. The term "strip-stock" as used herein is used generally to describe materials having very long lengths relative to their circumference and includes flexible pipe and tubing, wire, filaments, strands, webs, and the like.
Because of their relatively long length, strip-stock materials are generally unsuited for batch treatment processes in which the entire length of the article is treated simultaneously in a vaccum chamber containing a plasma. However, they may be located portion-wise by pushing or drawing the strip-stock material through a relatively short plasma treatment chamber within a treatment apparatus until the entire length has been treated. An apparatus for treating a roll of silicone tubing in this manner is disclosed in co-pending application Ser. No. 07/754,326. In that application, a motor driven reel and pulley system is used to draw a length of tubing from a feed reel into and through a plasma generated in a region of the apparatus and then winding the tubing up on a take-up reel as it comes out of the plasma generating region. The feed and take-up reels are located in a single evacuated vessel fed with a suitable gas, the same vessel having a pair of capacitively coupled plates to a RF source, the space between the plates serving as the plasma generating region.
An alternative construction for treatment of strip-stock is the commercially available PS1010 Plasma Treatment System, sold by Plasma Science, of Foster City, Calif.
In working with silicone tubing treated in the manner described in Ser. No. 07/754,326, it was subsequently discovered that the treatment process frequently produced reel-to-reel and place-to-place loss of clarity of the tubing material. As little as 10% of the treated length of the roll of clear silicone tubing retained its original clarity using the apparatus of Ser. No. 07/754,326. This loss of clarity created a problem in the manufacture of pacemaker leads, making it difficult to inspect the leads after assembly.
Investigations by the inventors of the present invention resulted in the discovery that the loss of clarity problem is associated with the change in the topography of the surface of the substrate after treatment, and the topography changes were attributable to differences in the tension on the tubing within the plasma treatment zone of the apparatus from time to time. This last discovery has, in turn, now lead to the development of the instant invention as described herein.